Farmers in the United States operate over 2 million farms covering roughly one billion acres of land and producing hundreds of billions of dollars of crops each year. The farmers spend tens of billions of dollars per year on seeds, fertilizer, chemicals and fuel. A modern farm is a complex operation where precision and efficiency can have a significant impact on the bottom line. According to the USDA, the most efficient 25% of US corn growers spend about $1 to grow a bushel of corn while growers in the least efficient 25% spend $3 to grow the same amount.
One way farmers improve efficiency is by avoiding unnecessary overlaps in tilling, spraying and harvesting operations. In other words, they avoid driving their tractors and equipment over the same area twice. Consider an 80-acre field and a 44-foot wide sprayer towed behind a tractor as an example. The sprayer is towed across the field in series of overlapping tracks. If the overlap between adjacent sprayer tracks is reduced from two feet to four inches four acres of spraying are eliminated. Such precision may be achieved by guiding tractors with global positioning system (GPS) based steering systems.
Precision control of passive, towed farm implements such as plows, rippers, disks, planters, applicators, drills and other equipment has other benefits as well. It makes it easier to operate machinery in dark or dusty conditions. Operators can drive faster and reduce driving stress. The quantity of fuel and chemicals used can be decreased, thereby saving money and the environment. Soil compaction can be avoided by keeping heavy equipment on precise tracks.
Advances in GPS technology (and systems based on other global navigational satellite systems (GNSS) such as the Russian GLONASS and the European GALILEO) have made it possible to drive large farm tractors along predetermined paths very accurately. A tractor can return to a field a year after first working it and follow the same track within an inch. The accuracy of a passive, towed implement is not as good, however.
A passive, towed implement does not have its own steering actuators. It is attached to a tractor by a hitch and the tractor pulls it across the ground. The implement may wander off its intended path for any number of reasons including asymmetrical loading (e.g. tougher ground to plow on one side than the other) or drag due to operating on a slope. Skilled tractor operators can compensate for a wandering implement by deliberately steering the tractor away from a desired path so that the implement stays on the path even though the tractor does not. However, despite the best efforts of operators, this manual method is imprecise, takes a long time and travel distance, and causes operator fatigue. It would be better if this “steering away” technique were automated and made more precise.
Modern tractors are often equipped with GPS (or, more generally, GNSS) based autopilot systems. These systems are capable of driving a tractor along a desired path with high accuracy. Further, it is common for such systems to accept offset commands. For example, one may command the system to drive the tractor a specific number of inches left or right of the programmed path. The tractor then travels parallel to, but offset from, the programmed path. Such lateral offsets are called “nudges”.
A wide variety of tractor and autopilot systems are available from different manufacturers. Each of these uses its own control strategy and implementation. However, the competitiveness of the market ensures that the great majority of tractor—autopilot combinations offer path tracking accuracy and response to nudge commands that fall within easily quantifiable parameters.
What is needed is a control system that ensures that passive, towed implements follow their intended path and correct deviations from the path as quickly as possible. The system should operate in concert with an autopilot-controlled tractor without requiring detailed information about the autopilot or the tractor. In fact, the system should interact with the tractor's autopilot only through a nudge control input. Such a system would automate the tiring, tedious task of steering a tractor intentionally off path so as to keep an implement on path and improve the accuracy of the actual path followed by the implement.